The invention is directed to a motion picture camera with a film transport mechanism synchronously drivable by a central drive system, a rotating mirror shutter and a device for pulling out the unexposed film from a film-unwinding spool and returning the exposed film to a film-winding spool.
In known motion picture cameras of this type, the device for pulling out and returning the film consists of a single sprocket which is continuously driven and rigidly coupled to the drive system; the unexposed film entering the camera and the exposed film leaving the camera are both transported by this sprocket. The film transport for the picture-taking is driven intermittently, for example by means of a maltese cross drive, so as to transport the film frame-by-frame past the image window. In sound-synchronous photography, i.e., with sound movies, this transport proceeds at 24 or 25 frames per second.
In order to accommodate this intermittent film transport performed by the film transport mechanism to the continuous film transport performed by the sprocket, the film must be formed into loops ahead of and behind the film transport mechanism. When a frame is being exposed and the film at the image window is stationary, the loop ahead of the film transport mechanism grows larger and that behind the film transport mechanism grows smaller.
This necessitates a painstaking loading process of the film material into the camera, since the loops can only be of a certain limited size as a result of space limitations inside the camera. Moreover, it must be ensured, i.e., by hand manipulation or otherwise, that the frame of film lies precisely at the image window. This makes loading of the film into the camera complicated, and usually the loading must be repeated several times until the above-described conditions are simultaneously and exactly fulfilled. Upon each such repetition, the pressure rollers which hold the film against the sprocket must be released, and the transporting, track-engaging and holding pins of the film transport mechanism must be disengaged. Only then can the position of the film over the image window (also known as the frame mask), or the length of the loops, be changed.